With the increasing importance of the nematode, Caenorhabditis elegans, as a model system for behavioral and neurobiological research, details of the roles of sensory structures in eliciting behavioral responses must be resolved to increase the utility of the model system. This proposed work will conclusively establish the amphid sensilla as chemosensory receptors while defining the precise chemical stimuli detected by their exposed dendritic endings. Laser microbeam ablation will be employed to answer the question of whether the amphids can serve dual functions in the detection of both chemical and thermal stimuli. Included will be tests to determine the nature and extent of receptor or pathway sharing among confirmed amphid-detected stimuli. Consequently, a more complete understanding of the role of the amphids in chemotaxis and thermotaxis will be provided.